I'm worried that my mom has cancer?

For the past 3 or 4 weeks now my mom has been complaining of being generally “sick” – she seems to keep getting infections, which can range from a sore throat to a fever, etc. Her glands keep swelling up. She has a headache and is nauseous constantly. She’s complaining of being “achy” and her joints hurt. The thing that concerns me the most is she is tired all the time. She can’t keep her eyes open, can’t make dinner because all she wants to do is sleep. She is 46 years old and I think she’s in general good health, but I’m kind of freaking out about this because I have had cancer twice, one of which was acute leukemia and it sounds like she has a lot of the symptoms I did. I do tend to think everything is cancer – I guess it’s just a fear – but I am REALLY worried so I guess I’m just looking for your opinions and advice… :(